The original pattern calls for SSK and then K2together at opposite end of the knit rows, so decreasing 2 stitches every 2 rows..

And yes, I guess what I am wanting to do is to keep the rib in tact

I am wanting to shape it for the legs so decrease then increase (to an hour glass type shape) Perhaps I could cast off some stitches do do it? then cast on again? hmm.. MAybe I should stick with the original